Power transmission system of hybrid electric vehicle

ABSTRACT

A power transmission system of a hybrid electric vehicle may include an input shaft, an output shaft, a first planetary gear set having three rotation elements, a second planetary gear set having three rotation elements, a third planetary gear set, a first shaft, a second shaft, a third shaft, a fourth shaft, a fifth shaft, a sixth shaft, and a seventh rotational shaft such that the power transmission system can suppress conversion to an Engine (ENG) mode by providing sufficient power performance at the time of wide open throttle (WOT) launching and maximally use power of an engine at the time of conversion to a first Hybrid-Electric Vehicle (HEV) mode and a third HEV mode.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to and the benefit of KoreanPatent Application No. 10-2014-0097364 filed on Jul. 30, 2014, theentire contents of which is incorporated herein for all purposes by thisreference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a power transmission system of a hybridelectric vehicle, and more particularly, to a power transmission systemof a hybrid electric vehicle that can suppress conversion to an Engine(ENG) mode by providing sufficient power performance at the time of wideopen throttle (WOT) launching and maximally use power of an engine atthe time of conversion to a first Hybrid-Electric Vehicle (HEV) mode anda third HEV mode.

Description of Related Art

Eco-friendly technology of a vehicle is a core technology influencingsurvival of a future vehicle industry and advanced vehicle makers devoteall their might to developing eco-friendly vehicles for meetingenvironmental and fuel efficiency regulations.

As a result, the respective vehicle makers have developed an electricvehicle (EV), a hybrid electric vehicle (HEV), a fuel cell electricvehicle (FCEV), and the like as a future vehicle technology.

Since the future vehicle has various technological restrictions such asa weight and cost, the vehicle makers have paid attention to the hybridelectric vehicle as an alternative of a realistic problem for meetingexhaust gas regulations and improving fuel efficiency performance andhave entered into keen competition for commercializing the hybridelectric vehicle.

The hybrid electric vehicle is a vehicle using two or more powersources. Two or more power sources may be combined by various schemesand a gasoline engine or a diesel engine using the existing fossil fueland a motor/generator driven by electric energy are mixed and used asthe power sources.

In the hybrid electric vehicle, an EV mode in which the hybrid electricvehicle is driven by only the motor, an HEV mode using both the engineand the motor, and an ENG mode using only the engine can be implementedaccording to the combination of the engine and the motor.

Further, the hybrid electric vehicle can acquire a significant fuelefficiency enhancement effect as compared with the existing vehiclethrough idle stop of stopping the engine when the vehicle stops, fuelsaving by regenerative braking that drives a generator by using kineticenergy of the vehicle instead of braking by the existing friction whenthe vehicle is braked, and stores in a battery electric energy generatedat the time of driving the generator and reuses the stored electricenergy when driving the vehicle, and the like.

A power transmission system of the hybrid electric vehicle is classifiedinto a single-mode scheme and a multiple-mode scheme.

The single-mode scheme has an advantage that torque transmissionmechanisms such as a clutch and a brake for transmission control are notrequired, but disadvantages that when the vehicle travels at a highspeed, efficiency deteriorates, and as a result, the fuel efficiency islow and an additional torque increasing device is required to apply thesingle-mode scheme to large-sized vehicles.

The multiple mode scheme has advantages that when the vehicle is drivenat the high speed, the efficiency is high and torque can be designed toincrease, and as a result, the multiple-mode scheme can be applied tolarge and medium-sized vehicles.

As a result, in recent years, the multiple-mode scheme has primarilybeen adopted rather than the single-mode scheme and the resultingresearch has actively progressed.

The multiple-mode scheme power transmission system is configured toinclude a plurality of planetary gear sets, a plurality ofmotors/generators used as the motor and the generator, a plurality oftorque transmission mechanisms (friction elements) capable ofcontrolling rotating elements of the planetary gear sets, a battery usedas power sources of the motors/generators, and the like.

The multiple-mode scheme power transmission system has differentoperating mechanisms according to connection configurations of theplanetary gear sets, the motors/generators, and the torque transmissionmechanisms.

In addition, since the multiple-mode scheme power transmission systemhas characteristics that durability, power transmission efficiency, asize, and the like vary according to the connection configurations,research and development for implementing a power transmission systemwhich is stronger, has no power loss, and is compact has been continuedin a power transmission system of a hybrid electric vehicle.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing apower transmission system of a hybrid electric vehicle that can suppressconversion to an Engine (ENG) mode by providing sufficient powerperformance at the time of wide open throttle (WOT) launching andmaximally use power of an engine at the time of conversion to a firstHybrid-Electric Vehicle (HEV) mode and a third HEV mode.

The present invention has also been made in an effort to provide a powertransmission system of a hybrid electric vehicle that decreases anelectric load by increasing a weight of a mechanical power transmissionpath to allow large engine power to be used, substitutes an ENG mode atthe time of launching to decrease the number of mode conversion times,and minimizes a change in RPM of all rotating elements at the time ofmode conversion.

The present invention has also been made in an effort to provide a powertransmission system of a hybrid electric vehicle that can provide an ENGmode in which the vehicle can be driven without the electric load of amotor/generator for improving fuel efficiency at the time of high-speeddriving.

An aspect of the present invention provides a power transmission systemof a hybrid electric vehicle including an input shaft into which powerof an engine is input, an output shaft outputting transmitted rotationalpower through an output gear, a first planetary gear set having threerotation elements constituted by a first sun gear, a first planetarycarrier, and a first ring gear and disposed on the output shaft, asecond planetary gear set having three rotation elements constituted bya second sun gear, a second planetary carrier, and a second ring gearand disposed at a rear side of the first planetary gear set, a thirdplanetary gear set having three rotation elements constituted by a thirdsun gear, a third planetary carrier, and a third ring gear and disposedat a rear side of the second planetary gear set, a first rotationalshaft directly connected with a first motor/generator while directlyconnecting one rotation element among the rotation elements of the firstplanetary gear set and one rotation element among the rotation elementsof the second planetary gear set, a second rotational shaft directlyconnected with the output shaft while directly connecting one rotationelement of the first planetary gear set excepted from the rotationelements constituting the first rotational shaft and one rotationelement among the rotation elements of the third planetary gear set, athird rotational shaft directly connecting one rotation element of thefirst planetary gear set excepted from the rotation elementsconstituting the first and second rotational shafts and the input shaft,a fourth rotational shaft directly connecting one rotation element ofthe second planetary gear set excepted from the rotation elementsconstituting the first rotational shaft with a transmission housing, afifth rotational shaft constituted by one rotation element of the secondplanetary gear set excepted from the rotation elements constituting thefirst and fourth rotational shafts, a sixth rotational shaft directlyconnecting one rotation element of the third planetary gear set exceptedfrom the rotation elements constituting the second rotational shaft anda second motor/generator, a seventh rotational shaft selectivelyconnected with the transmission housing while selectively connecting onerotation element of the third planetary gear set excepted from therotation elements constituting the second and sixth rotational shaftsand the fifth rotational shaft, and three friction elements selectivelyconnecting the rotational shafts to each other or selectively connectingthe respective rotational shafts to the transmission housing.

Each of all of the first, second, and third planetary gear sets may beconfigured by a single pinion planetary gear set and may have a firstrotational shaft connected with the first motor/generator while directlyconnecting the first sun gear and the second ring gear, a secondrotational shaft directly connecting the first planetary carrier and thethird planetary carrier, a third rotational shaft connecting the firstring gear and the input shaft, a fourth rotational shaft connecting thesecond sun gear to the transmission housing, a fifth rotational shaftincluding the second planetary carrier, a sixth rotational shaftconnecting the third sun gear to the second motor/generator, and aseventh rotational shaft including the third ring gear.

Each of the three friction elements may include a first brakeselectively connecting the seventh rotational shaft with thetransmission housing, a first clutch as a direct joining means of thethird planetary gear set, which selectively connects the secondrotational shaft with the seventh rotational shaft, and a second clutchselectively connecting the fifth rotational shaft with the seventhrotational shaft.

In the case of the first and second clutches, and the first brake, in EVmode 1, the first brake may operate, in EV mode 2, the first clutch mayoperate, in HEV mode 1, the first brake may operate, in HEV mode 2, thefirst clutch may operate, in HEV mode 3, the second clutch may operate,in ENG mode 1, the first brake and the second clutch may operate, and inENG mode 2, the first and second clutches may operate.

Each of the three friction elements may include a first brakeselectively connecting the seventh rotational shaft with thetransmission housing, a first clutch as the direct joining means of thethird planetary gear set, which selectively connects the sixthrotational shaft with the seventh rotational shaft, and a second clutchselectively connecting the fifth rotational shaft with the seventhrotational shaft.

Each of the three friction elements may include a first brakeselectively connecting the seventh rotational shaft with thetransmission housing, a first clutch as the direct joining means of thethird planetary gear set, which selectively connects the secondrotational shaft with the sixth rotational shaft, and a second clutchselectively connecting the fifth rotational shaft with the seventhrotational shaft.

The first planetary gear set may be configured by a double pinionplanetary gear set, and each of the second and third planetary gear setsis configured by the single pinion planetary gear set and may have afirst rotational shaft connected with the first motor/generator whiledirectly connecting the first sun gear and the second ring gear, asecond rotational shaft directly connecting the first ring gear and thethird planetary carrier, a third rotational shaft connecting the firstplanetary carrier and the input shaft, a fourth rotational shaftconnecting the second sun gear to the transmission housing, a fifthrotational shaft including the second planetary carrier, a sixthrotational shaft connecting the third sun gear to the secondmotor/generator, and a seventh rotational shaft including the third ringgear.

Each of the first and third planetary gear sets may be configured by thesingle pinion planetary gear set, and the second planetary gear set isconfigured by a double pinion planetary gear set and may have a firstrotational shaft connected with the first motor/generator while directlyconnecting the first sun gear and the second planetary carrier, a secondrotational shaft directly connecting the first planetary carrier and thethird planetary carrier, a third rotational shaft connecting the firstring gear and the input shaft, a fourth rotational shaft connecting thesecond sun gear to the transmission housing, a fifth rotational shaftincluding the second ring gear, a sixth rotational shaft connecting thethird sun gear to the second motor/generator, and a seventh rotationalshaft including the third ring gear.

Each of the first and second planetary gear sets may be configured bythe single pinion planetary gear set, and the third planetary gear setis configured by the double pinion planetary gear set and may have afirst rotational shaft connected with the first motor/generator whiledirectly connecting the first sun gear and the second ring gear, asecond rotational shaft directly connecting the first planetary carrierand the third ring gear, a third rotational shaft connecting the firstring gear and the input shaft, a fourth rotational shaft connecting thesecond sun gear to the transmission housing, a fifth rotational shaftincluding the second planetary carrier, a sixth rotational shaftconnecting the third sun gear to the second motor/generator, and aseventh rotational shaft including the third planetary carrier.

According to an exemplary embodiment of the present invention, in anoverall configuration, two EV modes, three HEV modes, and two ENG modescan be implemented in a combination of three planetary gear sets, threefriction elements, and two motors/generators.

Further, a weight of a mechanical power transmission path can beincreased by transmitting larger torque than engine torque to an outputshaft and power of a larger engine than the same specification of afirst motor/generator can be used.

Since the larger torque than the engine torque can be transmitted to theoutput shaft, high-rotation driving having high engine power at the samevehicle speed is enabled at the time of WOT launching and a largeracceleration force can be achieved.

In addition, since the larger acceleration force can be achieved in theHEV mode than the ENG mode, the HEV mode need not be converted into theENG mode at the time of launching, and as a result, a relatively simplesystem can be configured and friction elements can be reduced dependingon mode reduction, thereby further increasing efficiency.

The vehicle can be driven without electric loads of first and secondmotor/generators by providing the ENG mode at the time of the high-speeddriving to improve fuel efficiency.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

FIG. 2 is an operation table for each of operation modes of frictionelements applied to the power transmission system according to thevarious exemplary embodiments of the present invention.

FIG. 3 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

FIG. 4 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

FIG. 5 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

FIG. 6 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

FIG. 7 is a configuration diagram of a power transmission systemaccording to various exemplary embodiments of the present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

However, parts which are not related with the description are omittedfor clearly describing the exemplary embodiment of the present inventionand like reference numerals refer to like or similar elements throughoutthe specification.

In the following description, dividing names of components into first,second, and the like is to divide the names because the names of thecomponents are the same as each other and an order thereof is notparticularly limited.

FIG. 1 is a configuration diagram of a power transmission systemaccording to a first exemplary embodiment of the present invention.

Referring to FIG. 1, the power transmission system according to theexemplary embodiment of the present invention is configured in acombination of first, second, and third planetary gear sets PG1, PG2,and PG3, first and second motors/generators MG1 and MG2, and threefriction elements BK1, CL1, and CL2.

The first planetary gear set PG1 as a single pinion planetary gear setincludes a first sun gear S1, a first ring gear R1, and a firstplanetary carrier PC1 that rotatably supports a plurality of firstpinions P1 which outer-engage with each other between the first sun gearS1 and the first ring gear R1.

The second planetary gear set PG2 as the single pinion planetary gearset includes a second sun gear S2, a second ring gear R2, and a secondplanetary carrier PC2 that rotatably supports a plurality of secondpinions P2 which outer-engage with each other between the second sungear S2 and the second ring gear R2.

The third planetary gear set PG3 as the single pinion planetary gear setincludes a third sun gear S3, a third ring gear R3, and a thirdplanetary carrier PC3 that rotatably supports a plurality of thirdpinions P3 which outer-engage with each other between the third sun gearS3 and the third ring gear R3.

The first, second, and third planetary gear sets PG1, PG2, and PG3 aresequentially disposed on an output shaft OS from an engine ENG and haveseven rotational shafts TM1 to TM7 while respective rotating elementsare directly joined or selectively connected to each other.

In more detail, the first, second, and third planetary gear sets PG1,PG2, and PG3 have the seven rotational shafts TM1 to TM7 while the firstsun gear S1 of the first planetary gear set PG1 is directly connectedwith the second ring gear R2 of the second planetary gear set PG2, thesecond planetary carrier PC2 of the second planetary gear set PG2 isselectively connected with the third ring gear R3 of the third planetarygear set PG3, and the third planetary carrier PC3 of the third planetarygear set PG3 is directly connected with the first planetary carrier PC1of the first planetary gear set PG1.

The first rotational shaft TM1 is configured by connecting the first sungear S1 and the second ring gear R2 and directly connected with thefirst motor/generator MG1.

The second rotational shaft TM2 is configured by connecting the firstplanetary carrier PC1 and the third planetary carrier PC3, and directlyconnected with the output shaft OS to continuously operate as an outputelement.

The third rotational shaft TM3 includes the first ring gear R1, and isdirectly connected with an input shaft IS to continuously operate as aninput element.

The fourth rotational shaft TM4 includes the second sun gear S2, and isdirectly connected with a transmission housing H to continuously operateas a fixation element.

The fifth rotational shaft TM5 includes the second planetary carrierPC2.

The sixth rotational shaft TM6 includes the third sun gear S3 and isdirectly connected with the second motor/generator MG2.

The seventh rotational shaft TM7 includes the third ring gear R3, and isselectively connected with the transmission housing H.

The first motor/generator MG1 and the second motor/generator MG2 asindependent power sources have functions as the motor and the generatoras described above.

The first motor/generator MG1 operates as a motor that is directlyconnected with the first rotational shaft TM1 to supply rotational poweror serves as a generator that generates electricity while rotating byrotational force of the first rotational shaft TM1.

The second motor/generator MG2 operates as a motor that is directlyconnected with the sixth rotational shaft TM6 to supply rotational poweror serves as a generator that generates electricity while rotating byrotational force of the sixth rotational shaft TM6.

The first brake BK1 among the friction elements is a friction elementthat selectively connects a rotation element and a fixation element(transmission housing), and the first and second clutches CL1 and CL2 asfriction elements that selectively connect the rotation element and thefixation element may include multi-disk type hydraulic friction elementsthat are friction joined to each other by hydraulic pressure.

The first brake BK1 is disposed to selectively connect the thirdrotational shaft TM7 and the transmission housing H, and as a result,the seventh rotational shaft TM7 may selectively operate as the fixationelement.

The first clutch CL1 connects three rotation elements of the thirdplanetary gear set PG3 to each other by two rotational shafts of threerotational shafts TM2, TM6, and TM7 including three rotation elements ofthe third planetary gear set PG3 to allow the third planetary gear setPG3 to be directly joined and in the first exemplary embodiment based onFIG. 1, it is disclosed that the first clutch CL1 is disposed betweenthe second rotational shaft TM2 and the seventh rotational shaft TM7 andthe second clutch CL2 selectively connects the fifth rotational shaftTM5 and the seventh rotational shaft TM7.

In FIG. 1, it is disclosed that the engine ENG is disposed at a frontside of the first planetary gear set PG1, but the present invention isnot limited thereto and the engine ENG may be disposed at a rear side ofthe third planetary gear set PG3.

FIG. 2 is an operation table for each of operation modes of frictionelements applied to the power transmission system according to the firstexemplary embodiment of the present invention.

Referring to FIG. 2, operation states of the friction elements for eachoperation mode will be described below.

In Electric Vehicle (EV) mode 1, the first brake BK1 operates, in EVmode 2, the first clutch CL1 operates, in Hybrid-Electric Vehicle (HEV)mode 1, the first brake BK1 operates, in HEV mode 2, the first clutchCL1 operates, in HEV mode 3, the second clutch CL2 operates, in Engine(ENG) mode 1, the first brake BK1 and the second clutch CL2 operate, andin ENG mode 2, the first and second clutches CL1 and CL2 operate.

As described above, the power transmission system according to the firstexemplary embodiment of the present invention may implement two EVmodes, three HEV modes, and two ENG modes.

Hereinafter, an operation principle for each mode will be describedbelow.

[EV Mode 1]

The EV mode is a mode that drives the vehicle with power of themotor/generator by supplying power of a battery to the motor/generatorwhile the engine stops.

The EV mode exerts a large influence on fuel efficiency improvementbecause the engine stops, has an advantage that the vehicle may bedriven backward without an additional backward device, operates at thetime of starting and low-speed driving after stopping, and requires adeceleration transmission ratio in which a power source rotates morerapidly than an output member for slip-down prevention or rapidacceleration on a slope.

Under such a condition, in EV mode 1, the second motor/generator MG2 isoperation-controlled while the seventh rotational shaft TM7 operates asthe fixation element by operating the first brake BK1, and as a result,a deceleration output is performed according to a gear ratio of thethird planetary gear set PG3 while an input in the sixth rotationalshaft TM6 is performed.

[EV Mode 2]

The motor/generator has characteristics that the efficiency depends on arotational speed and torque and this means that a ratio of the electricenergy is converted into mechanical energy of rotation and torque varieseven though the same current is supplied.

That is, current of the battery used in the EV mode is energyaccumulated by combustion of fuel or regenerative braking in the engineand efficiently using the accumulated energy regardless of a generationpath is directly linked with fuel efficiency improvement.

Due to such a reason, in recent years, there has been a tendency that atransmission having two or more steps is mounted even in an electricvehicle and since it is advantageous that two or more transmission stepsare provided in the EV mode of the hybrid electric vehicle, EV mode 2 isprovided even in the exemplary embodiment of the present invention.

When a transmission process of EV mode 2 is examined by considering sucha point, a vehicle speed increases to cancel the operation of the firstbrake BK1 at a point in which the efficiency of the secondmotor/generator MG2 is low, and the first clutch CL1 isoperation-controlled, during driving in EV mode 1 in EV mode 2.

Then, since the first clutch CL1 which is a direct joining means of thethird planetary gear set PG3 operates, the third planetary gear set PG3is in a direct joining state, and as a result, while the second, sixth,and seventh rotational shafts rotate at the same speed, the input isjust output.

[HEV Mode 1]

In HEV mode 1, the power of the engine is transmitted to the outputmember through a mechanical path and an electric path, the power isdistributed by the planetary gear set, and since the engine and themotor/generator connected to the planetary gear set may arbitrarilycontrol the rotational speed regardless of the vehicle speed, the engineand the motor/generator serve as an electronic continuously variabletransmission.

Accordingly, an engine speed and torque is fixed to with respect to agiven vehicle speed in the existing transmission, while the electroniccontinuously variable transmission may arbitrarily change the enginespeed and the torque, driving efficiency of the engine may be maximizedand fuel efficiency improvement may be achieved.

By considering such a point, in EV mode 1, the second rotational shaftTM2 is restrained in connection with the output shaft OS and theresidual first and third rotational shafts TM1 and TM3 are rotatable inthe first planetary gear set PG1.

Therefore, after the engine ENG starts by using the firstmotor/generator MG1, the speeds of the engine ENG and the firstmotor/generator MG1 may be controlled regardless of the vehicle speed.

Further, since torque of the first motor/generator MG1 is appliedclockwise regardless of the rotational direction, the sum of the torquesof the engine ENG and the first motor/generator MG1 are transmitted tothe output shaft to generate high drive power.

In addition, when the first motor/generator MG1 rotatescounterclockwise, the first motor/generator MG1 serves as the generator,and when the first motor/generator MG1 rotates clockwise (of course, inthis case, the rotation speed of the engine ENG is lower than before),the first motor/generator MG1 serves as the motor.

Since the engine ENG and the first motor/generator MG1 may becontinuously variably controlled as necessary in HEV mode 1 (inputbranch), HEV mode 1 may show very excellent performance in terms of fuelefficiency and power performance.

[HEV Mode 2]

In an exemplary embodiment of the present invention, the input branchmode may be set as two types, a rotational speed ratio of the engine andthe motor/generator to the vehicle speed may be, in overall, set as twotypes by changing a gear ratio of the second planetary gear set PG2, anda rotational speed level for each rotation element deteriorates inoverall to assist the fuel efficiency improvement.

In EV mode 2, the second rotational shaft TM2 of the first planetarygear set PG1 is restrained in connection with the output shaft OS andthe residual first and third rotational shafts TM1 and TM3 arerotatable.

Therefore, when the engine ENG and the first motor/generator MG1 arecontrolled, the speeds of the engine ENG and the first motor/generatorMG1 may be continuously variably controlled regardless of the vehiclespeed.

In addition, when the first motor/generator MG1 rotatescounterclockwise, the first motor/generator MG1 serves as the generator,and when the first motor/generator MG1 rotates clockwise (of course, inthis case, the rotation speed of the engine ENG is lower than before),the first motor/generator MG1 serves as the motor.

As such, since the engine ENG and the first motor/generator MG1 may becontinuously variably controlled as necessary, EV mode 2 may show veryexcellent performance in terms of fuel efficiency and power performance.

[HEV Mode 3]

In an HEV input branch mode, the rotation speed of the motor/generatorconnected to the output member is restrained to the vehicle speed, andas a result, it is difficult to efficiently operate the motor/generatorand decrease a capacity of the motor/generator.

In particular, when the vehicle speed is high and the rotation speed ofthe motor/generator restrained to the vehicle speed is thus high, theefficiency of the motor/generator deteriorates, and as a result, optimalfuel efficiency may not be implemented.

Under such a condition, when the first planetary gear set PG1 connectedwith the engine ENG and two different elements of the second planetarygear set PG2 connected with an output gear OG are joined to each otherto control the rotational speeds of the engine ENG and twomotors/generators MG1 and MG2 regardless of the vehicle speed, afunction of the continuously variable transmission operates once againto achieve the fuel efficiency improvement.

As a result, when the second clutch CL2 operates, the speed and thetorque of the second motor/generator MG2 is restrained by the speed andthe torque of the engine ENG through the second planetary gear set PG2,and since the first planetary gear set PG1 and the third planetary gearset PG3 are connected to each other by the second rotational shaft TM2,the speeds and the torques are restrained from each other.

In addition, the first and second motors/generators MG1 and MG2 need tohave an electric energy balance to each other, and while all rotationelements of the first and third planetary gear sets PG1 and PG3 arecorrelated to each other in terms of the speed and the torque, thefunction of the electronic continuously variable transmission isperformed.

[ENG Mode 1]

Core technology for the fuel efficiency improvement of the hybridelectric vehicle may be recovery and reuse of regenerative energy andarbitrary control of an engine operation point.

In addition, the control of the engine operation point accompanies twoenergy conversion processes of a process in which the mechanical energyof the engine is converted into the electric energy in themotor/generator and a process in which the electric energy of themotor/generator is converted into the mechanical energy again in themotor/generator again.

During the energy conversion, total energy is not output, the loss isgenerated in the middle of the conversion, and under a predetermineddriving condition, the fuel efficiency may be more excellent in the ENGmode in which the vehicle is driven by only the engine than the hybridoperation mode.

That is, in ENG mode 1, when the first brake BK1 and the second clutchCL2 are coupled to each other, the power of the engine ENG istransmitted to the output shaft OS through the second rotational shaftTM2 while the first rotational shaft TM1 stops and the seventhrotational shaft TM7 stops, the deceleration transmission ratio isformed.

In this case, since the power of the first and second motors/generatorsMG1 and MG2 is not required, the ENG mode in which the vehicle is drivenby only the power of the engine is established.

[ENG Mode 2]

In ENG mode 2, when the first clutch CL1 and the second clutch CL2 arecoupled to each other, all rotation elements of the third planetary gearset PG3 integrally rotate, and as a result, the seventh rotational shaftTM7 rotates at the same speed as the output and the second rotationalshaft TM1 is accelerated to rotate according to a gear ratio of thesecond planetary gear set PG2.

Further, the first rotational shaft TM1 connected with the engine ENGrotates at a lower speed than the second rotational shaft TM2, and as aresult, an acceleration transmission ratio is formed.

In this case, since the power of the first and second motors/generatorsMG1 and MG2 is not required, the ENG mode in which the vehicle is drivenby only the power of the engine is established.

As described above, according to the first exemplary embodiment of thepresent invention, in an overall configuration, two EV modes, three HEVmodes, and two ENG modes may be implemented in a combination of threeplanetary gear sets PG1, PG2, and PG3, three friction elements BK1, CL1,and CL2, and two motors/generators MG1 and MG2.

Further, in the first exemplary embodiment of the present invention, thepower of the engine ENG is input into the first ring gear R1 of firstplanetary gear set and the power of the first motor/generator MG1 isinput into the first sun gear S1, and as a result, torque which islarger than the torque of the engine ENG is transmitted to the outputshaft OS to increase a weight of a mechanical power transmission pathand use larger engine power for the same specification of the firstmotor/generator MG1.

Further, in the first exemplary embodiment of the present invention,since the larger torque than the engine torque may be transmitted to theoutput shaft, high-rotation driving having high engine power at the samevehicle speed is enabled at the time of WOT launching and a largeracceleration force may be achieved.

In addition, in the first exemplary embodiment of the present invention,since the larger acceleration force may be achieved in the HEV mode thanthe ENG mode, the HEV mode need not be converted into the ENG mode atthe time of launching, and as a result, a relatively simple system maybe configured and friction elements may be reduced depending on modereduction, thereby further increasing efficiency.

The vehicle may be driven without the electric load of the first andsecond motor/generators by providing the ENG mode at the time of thehigh-speed driving to improve fuel efficiency.

FIG. 3 is a configuration diagram of a power transmission systemaccording to a second exemplary embodiment of the present invention.

Referring to FIG. 3, in the first exemplary embodiment, the first clutchCL1 which is the direct joining means of the third planetary gear setPG3 is disposed between the first rotational shaft TM2 and the seventhrotational shaft TM7, but in the second exemplary embodiment, the firstclutch CL1 which is the direct joining means of the third planetary gearset PG3 is disposed between the sixth rotational shaft TM6 and theseventh rotational shaft TM7.

Since the second exemplary embodiment is different from the firstexemplary embodiment only in a layout position of the first clutch CL1and the second exemplary embodiment is the same as the first exemplaryembodiment in an operation effect, a detailed description thereof willbe omitted.

FIG. 4 is a configuration diagram of a power transmission systemaccording to a third exemplary embodiment of the present invention.

Referring to FIG. 4, in the first exemplary embodiment, the first clutchCL1 which is the direct joining means of the third planetary gear setPG3 is disposed between the second rotational shaft TM2 and the seventhrotational shaft TM7, but in the second exemplary embodiment, the firstclutch CL1 which is the direct joining means of the third planetary gearset PG3 is disposed between the second rotational shaft TM2 and thesixth rotational shaft TM6.

Since the third exemplary embodiment is different from the firstexemplary embodiment only in the layout position of the first clutch CL1and the second exemplary embodiment is the same as the first exemplaryembodiment in the operation effect, a detailed description thereof willbe omitted.

FIG. 5 is a configuration diagram of a power transmission systemaccording to a fourth exemplary embodiment of the present invention.

Referring to FIG. 5, in the first exemplary embodiment, the firstplanetary gear set PG1 is configured by a single pinion planetary gearset, but in the fourth exemplary embodiment, the first planetary gearset PG1 is configured by a double-pinion planetary gear set.

As a result, the first rotational shaft TM1 related with the firstplanetary gear set PG1 is configured by connecting the first sun gear S1and the second ring gear R2, the second rotational shaft TM2 isconfigured by connecting the first ring gear R1 and the third planetarycarrier PC3, and the third rotational shaft TM3 is configured to includethe first planetary carrier PC1.

Since the fourth exemplary embodiment is different from the firstexemplary embodiment only in configurations of the second and thirdrotational shafts TM2 and TM3 and the fourth exemplary embodiment is thesame as the first exemplary embodiment in the operation effect, adetailed description thereof will be omitted.

FIG. 6 is a configuration diagram of a power transmission systemaccording to a fifth exemplary embodiment of the present invention.

Referring to FIG. 6, in the first exemplary embodiment, the secondplanetary gear set PG2 is configured by the single pinion planetary gearset, but in the fifth exemplary embodiment, the second planetary gearset PG2 is configured by the double-pinion planetary gear set.

As a result, the first rotational shaft TM1 related with the secondplanetary gear set PG2 is configured by connecting the first sun gear S1and the second planetary carrier PC2, the fourth rotational shaft TM4 isconfigured to include the second sun gear S2, and the fifth rotationalshaft TM5 is configured to include the second ring gear R2.

Since the fifth exemplary embodiment is different from the firstexemplary embodiment only in configurations of the first and fifthrotational shafts TM1 and TM5 and the fifth exemplary embodiment is thesame as the first exemplary embodiment in the operation effect, adetailed description thereof will be omitted.

FIG. 7 is a configuration diagram of a power transmission systemaccording to a sixth exemplary embodiment of the present invention.

Referring to FIG. 7, the third planetary gear set PG3 is configured bythe single pinion planetary gear set in the first exemplary embodiment,but the third planetary gear set PG3 is configured by the double-pinionplanetary gear set in the sixth exemplary embodiment.

As a result, the second rotational shaft TM2 related with the thirdplanetary gear set PG3 is configured by connecting the first planetarycarrier PC1 and the third ring gear R3, the sixth rotational shaft TM6is configured to include the third sun gear S3, and the seventhrotational shaft TM7 is configured to include the third planetarycarrier PC3.

Since the fifth exemplary embodiment is different from the firstexemplary embodiment only in configurations of the second and seventhrotational shafts TM2 and TM7 and the fifth exemplary embodiment is thesame as the first exemplary embodiment in the operation effect, adetailed description thereof will be omitted.

For convenience in explanation and accurate definition in the appendedclaims, the terms “upper”, “lower”, “inner” and “outer” are used todescribe features of the exemplary embodiments with reference to thepositions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings as well as various alternatives and modifications thereof. Itis intended that the scope of the invention be defined by the Claimsappended hereto and their equivalents.

What is claimed is:
 1. A power transmission system of a hybrid electricvehicle, comprising: an input shaft into which power of an engine isinput; an output shaft outputting transmitted rotational power throughan output gear; a first planetary gear set having three rotatableelements having a first sun gear, a first planetary carrier, and a firstring gear; a second planetary gear set having three rotatable elementshaving a second sun gear, a second planetary carrier, and a second ringgear; a third planetary gear set having three rotatable elements havinga third sun gear, a third planetary carrier, and a third ring gear; afirst shaft directly connected with a first motor/generator whiledirectly connecting one rotatable element among the rotatable elementsof the first planetary gear set and one rotatable element among therotatable elements of the second planetary gear set; a second shaftdirectly connected with the output shaft while directly connectinganother rotatable element of the first planetary gear set and onerotatable element among the rotatable elements of the third planetarygear set; a third shaft directly connecting a remaining rotatableelement of the first planetary gear set and the input shaft; a fourthshaft directly connecting another rotatable element of the secondplanetary gear set with a transmission housing; a fifth shaft directlyconnected to a remaining rotatable element of the second planetary gearset; a sixth shaft directly connecting another rotatable element of thethird planetary gear set and a second motor/generator; and a seventhshaft selectively connectable with the transmission housing whileselectively connecting the one rotatable element of the third planetarygear set shaft.
 2. The system of claim 1, wherein each of all of thefirst, second, and third planetary gear sets is a single pinionplanetary gear set, and wherein the first shaft is directly connectedwith the first motor/generator while directly connecting the first sungear and the second ring gear, the second shaft directly connects thefirst planetary carrier and the third planetary carrier, the third shaftdirectly connects the first ring gear and the input shaft, the fourthshaft directly connects the second sun gear to the transmission housing,the fifth shaft is directly connected to the second planetary carrier,the sixth shaft directly connects the third sun gear to the secondmotor/generator, and the seventh shaft is directly connected to thethird ring gear.
 3. The system of claim 1, further comprising: a firstbrake to selectively connect the seventh shaft with the transmissionhousing; a first clutch to selectively lock the third planetary gear setby selectively connecting the second shaft with the seventh shaft; and asecond clutch to selectively connect the fifth shaft with the seventhshaft.
 4. The system of claim 1, further comprising: a first brakeselectively connecting the seventh shaft with the transmission housing;a first clutch to selectively lock the third planetary gear set byselectively connecting the sixth shaft with the seventh shaft; and asecond clutch selectively connecting the fifth shaft with the seventhshaft.
 5. The system of claim 1, further comprising: a first brakeselectively connecting the seventh shaft with the transmission housing;a first clutch to selectively lock the third planetary gear set byselectively connecting the second shaft with the sixth shaft; and asecond clutch selectively connecting the fifth shaft with the seventhshaft.
 6. The system of claim 1, wherein the first planetary gear set isa double pinion planetary gear set, and each of the second and thirdplanetary gear sets is a single pinion planetary gear set and has thefirst shaft directly connected with the first motor/generator whiledirectly connecting the first sun gear and the second ring gear, thesecond shaft directly connecting the first ring gear and the thirdplanetary carrier, the third shaft directly connecting the firstplanetary carrier and the input shaft, the fourth shaft directlyconnecting the second sun gear to the transmission housing, the fifthshaft including the second planetary carrier, the sixth shaft directlyconnecting the third sun gear to the second motor/generator, and theseventh shaft including the third ring gear.
 7. The system of claim 1,wherein each of the first and third planetary gear sets is a singlepinion planetary gear set, and the second planetary gear set is a doublepinion planetary gear set and has the first shaft directly connectedwith the first motor/generator while directly connecting the first sungear and the second planetary carrier, the second shaft directlyconnecting the first planetary carrier and the third planetary carrier,the third shaft directly connecting the first ring gear and the inputshaft, the fourth shaft connecting the second sun gear to thetransmission housing, the fifth shaft including the second ring gear,the sixth shaft directly connecting the third sun gear to the secondmotor/generator, and the seventh shaft including the third ring gear. 8.The system of claim 1, wherein each of the first and second planetarygear sets is a single pinion planetary gear set, and the third planetarygear set is a double pinion planetary gear set and has the first shaftdirectly connected with the first motor/generator while directlyconnecting the first sun gear and the second ring gear, the second shaftdirectly connecting the first planetary carrier and the third ring gear,the third shaft connecting the first ring gear and the input shaft, thefourth shaft directly connecting the second sun gear to the transmissionhousing, the fifth shaft including the second planetary carrier, thesixth shaft connecting the third sun gear to the second motor/generator,and the seventh shaft including the third planetary carrier.
 9. A powertransmission system of a hybrid electric vehicle, comprising: an inputshaft into which power of an engine is input; an output shaft outputtingtransmitted rotational power through an output gear; a first planetarygear set as a first single pinion planetary gear set having threerotatable elements including a first sun gear, a first planetarycarrier, and a first ring gear; a second planetary gear set as a secondsingle pinion planetary gear set having three rotatable elementsincluding a second sun gear, a second planetary carrier, and a secondring gear; a third planetary gear set as a third single pinion planetarygear set having three rotatable elements including a third sun gear, athird planetary carrier, and a third ring; a first shaft directlyconnected with a first motor/generator while directly connecting thefirst sun gear and the second ring gear; a second shaft directlyconnecting the first planetary carrier and the third planetary carrierand directly connected with the output shaft; a third shaft directlyconnecting the first ring gear and the input shaft; a fourth shaftdirectly connecting the second sun gear to a transmission housing; afifth shaft directly connected to the second planetary carrier; a sixthshaft directly connecting the third sun gear to the secondmotor/generator; and a seventh shaft directly connected to the thirdring gear, and selectively connectable with the fifth shaft andselectively connectable with the transmission housing.
 10. The system ofclaim 9, further comprising: a first brake to selectively connect theseventh shaft with the transmission housing; a first clutch toselectively lock the third planetary gear set by selectively connectingthe second shaft with the seventh shaft; and a second clutch toselectively connect the fifth shaft with the seventh shaft.
 11. Thesystem of claim 9, further comprising: a first brake selectivelyconnecting the seventh shaft with the transmission housing; a firstclutch to selectively lock the third planetary gear set by selectivelyconnecting the sixth shaft with the seventh shaft; and a second clutchselectively connecting the fifth shaft with the seventh shaft.
 12. Thesystem of claim 9, further comprising: a first brake selectivelyconnecting the seventh shaft with the transmission housing; a firstclutch to selectively lock the third planetary gear set by selectivelyconnecting the second shaft with the sixth shaft; and a second clutchselectively connecting the fifth shaft with the seventh shaft.